The present invention relates to electromagnetic transducers for information storage and retrieval systems, such as disk or tape drives.
Current commercially available disk drives employ magnetoresistive (MR) sensors for reading data, and store data in domains having magnetizations that are substantially parallel to concentric media tracks, the parallel magnetic storage sometimes called longitudinal recording. It has been predicted that such longitudinal magnetic storage will become unstable at normal operating conditions when the domains reach a minimal size, termed the superparamagnetic limit. In order to store the data at higher density, the drive system may instead be designed to store data in domains that are substantially perpendicular to the disk surface, which may be termed perpendicular recording.
Prior art systems for perpendicular recording include an inductive transducer positioned in close proximity to a surface of a disk. The inductive transducer has a U-shaped core formed of high-permeability, low-coercivity or xe2x80x9csoftxe2x80x9d magnetic material and the media has a soft magnetic underlayer, the core and underlayer forming a magnetic circuit that traverses a higher coercivity media layer, for magnetizing the media layer or reading the magnetization of the media layer. The core has magnetic pole tips that differ in area so that the magnetic signal is concentrated in the smaller pole tip for reading or writing data. The pole tips are sufficiently separated to encourage magnetic flux to travel through the media, instead of across a submicron nonmagnetic gap that is typically employed for longitudinal recording.
MR sensors sense a change in magnetic field at the sensor with a change in resistance of the sensor, which may be measured as a change in current or voltage across the sensor. In an attempt to limit the sensing of a MR sensor to the individual bit directly adjacent the sensor, magnetic shields are disposed in the transducer adjacent the sense element, shielding the sense element from the magnetic fields emanating from adjacent bits.
The present inventors have discovered, however, that the shields can form a magnetic circuit with the media underlayer used in perpendicular recording, causing problems in reading and writing. Moreover, the relatively large distance between the trailing perpendicular recording pole tip and a MR sensor disposed on an opposite side of the flux return pole tip can cause misalignment of the MR sensor and the recording pole tip. In addition, increasing the density of bits on each track and the disk speed requires higher frequency recording, for which inductance of the coils and core may become problematic.
In accordance with the present invention, embodiments of a merged perpendicular recording and magnetoresistive sensing transducer are disclosed in which the magnetic influence of the recording transducer on the sense transducer and the shields is reduced. As one example, the magnetic flux produced by the recording coil may be essentially zero at the sense transducer. Another advantage of the invention is that the inductance of the coils used to generate magnetic flux in the recording transducer is reduced, facilitating high-frequency operation. Moreover, the magnetic flux generated by the core and transmitted by the recording pole tip may be increased, improving recording capabilities. In brief, various embodiments of a merged transducer are disclosed having increased recording flux, reduced inductance and reduced influence of the recording elements on the sensing elements, for greatly improved performance.